The present invention relates to manhole cover assemblies for pressure vessels, and, more particularly, to a quick opening manhole cover assembly which is suitable for use with any shape manhole cover.
Pressure vessels are well known in the art and are used, for example, by the chemical and food industry to process various chemicals and food stuffs. These vessels generally range in size from capacities of a few hundred gallons to several thousand gallons, and can be constructed to withstand internal pressures of several atmospheres. The vessels may be constructed of glass lined steel or of a corrosive-resistant material such as stainless steel.
It is common to provide such vessels with manholes to permit entry into the vessel for cleaning and inspection. Usually, the cover for such a manhole is clamped directly to a flange surrounding the manhole opening. The clamps are sized to withstand the load necessary to compress a gasket between the manhole cover and the flange in order to obtain a leak-free joint. It is not uncommon to use many large clamps in order to distribute the load evenly about the manhole cover and to use a hand tool, such as a wrench, to individually tighten each clamp. Use of a hand tool can result in overtightening that could cause distortion of the flange and damage to the glass lining of the vessel. For example, such clamps could drop into the vessel and damage the glass lining.
Clamp-type covers are also time-consuming to open and close, since each clamp has to be individually wrench tightened several times to properly seat the gasket. This procedure could take as long as an hour depending upon the size of the manhole, the number of clamps used and the pressures expected within the vessel. Conversely, to open the manhole cover, each clamp has to be loosened and removed.
In a successful attempt to solve the above-identified problems, a quick opening manhole cover assembly was invented and patented in U.S. Pat. No. 4,279,356 (Amorese and Piarulli). The invention of this patent provides a quick opening manhole cover assembly where the manhole cover can be opened or closed very quickly and where no clamps are used to compress a gasket between the manhole cover and the vessel. The patented invention includes a sealing means which comprises a plurality of ears of a locking ring engaged beneath a collar in horizontal arcuate grooves. Due to the nature and geometry of the sealing means, the patented invention is only suitable for use with round manhole covers. This is unfortunate in that not all manhole covers are round. For example, many covers for intermediate capacity vessels (500-2000 gallons) are elliptical in shape. It is conceivable that covers of other shapes may also be employed.
What is needed, then, is a quick opening manhole cover assembly for use with virtually any shape cover.